Wave guides for propagation of high frequency wave energy



y 1961 J. M. LAMB 2,991,434

WAVE GUIDES FOR PROPAGATION OF HIGH FREQUENCY WAVE ENERGY Original FiledMay 51, 1947 INVENTOR, 2,. m

Aaewr United States Patent 2 Claims. (Cl. 333-95) This invention relatesto improvements in flexible wave guides for the propagation of highfrequency wave energy and in the art of producing flexible wave guidesfrom flat stock. The invention is directed particularly to flexible waveguides suitable for making connection between rigid wave guides or otherelements of an ultra high frequency transmission line.

The present application is a continuation of my copending application,Serial No. 257,581, filed November 21, 1951, now abandoned, which inturn is a division of my application, Serial No. 751,561, filed May 31,1947, now Patent No. 2,600,169, issued June 10, 1952.

Known flexible wave guides consist of rectangular metal tubes havingcorrugated side walls, the flexibility being imparted to the tube bybending permitted in the walls of the corrugations. One guide of thistype is made by winding a formed metal strip helically over arectangular arbor, then suitably engaging adjacent edges of the strip toform a seam on the outside or inside of the corrugation. In guides ofthis description, mechanical difliculties are encountered in theattachment of fittings thereto by reason of the configuration of thehelix at the plane where cut-ofiis effected. A non-symmetricalterminating surface results and this irregularity creates objectionablemechanical characteristics. An added disadvantage of the helical woundflexible wave guide resides in the electrical losses from the resistanceand surface discontinuity of the seam, where the adjacent convolutionsare interengaged to form the continuous tube.

In another form of flexible wave guide, corrugations are formed in aseamless rectangular tube by expanding the tube transversely at spacedlocations along its axis. Basic seamless tubes for this formof waveguide must be fabricated of metal with a high percentage of elongationin order to permit the stretch necessary to corrugation depth whichprovides flexibility without distortion of the rectangularconfiguration; and this is a limitation which becomes more acute as thephysical dimensions of the wave guide increase. With the trend to use ofhigher power for long range applications flexible seamless types of waveguides are not available; and correspondingly large wave guides havinglong dimensions of from six to twenty-one inches are required to meetthese increasing requirements.

A further disadvantage of the seamless type of flexible wave guide, andparticularly of utilizing extremes of elongation in metals of whichflexible guides are normally made, is the tendency to minute cracking ofthe stretched side walls at location of non-uniformity of the tube.While failures of this kind may not present problems at atmosphericpressure, they do preclude eflicient pressurizing of the guide inaccordance with practices in the ultra high frequency art.

Some flexible corrugated wave guides are fabricated by re-forming arectangular, extruded, seamless tube as, for example, the one disclosedin US. Patent No. 2,563,- 578, issued August 7, 1951, to Candee. To makea guide of this nature, a tube of appropriate rectangular dimension isfirst produced then annularly corrugated step by step by stretching theside walls and radius corners to ICE meet the desired configuration.This process is limited to relatively small wave guides the tubing forwhich does not exceed the size of known extruders and sizes which arewithin the limits of the stretching of material to meet the requiredcorrugation depth which provides the flexibility. Brass is aconventional material for waveguides and, while wave guides arecurrently used in sizes of the range of 11.5 inches deep by 23 inchesacross, the units of diameter'for known seamless-drawn tubing of cuprousalloys is in the range of 8-10 inches. Likewise, to meet the requiredflexibility, the stretching requirement of the cuprous alloy for largerwave guides made from seamless tubing is far beyond the 50% limit ofelongation for themost ductile cuprous alloys. While the annularcorrugations of the Candee wave guide are superior to the helicalcorrugations of earlier flexible units, these limitations, in the faceof ever increasing sizes, are detrimental to the overall utility of sucha seamless product.

To overcome difiiculties of this kind, I provide an improved flexibleguide formed from a relatively thin, wide, continuous flat strip whichis corrugated, folded and seamed to rectangular shape, the corrugationsbeing disposed in theside walls at right angles to the longitudinal axisof the guide. In the use of this construction, it is possible to takeadvantage of the desirable flexing characteristics of a guidehaving'corrugated side walls and at the same time to retain the superiorconstruction outlined above which is free from a helical configurationand which may be obtained within the physical units of stand ardcommercial materials and using readily available rolled stock sizes. Ilocate the seam of my flexible guide at the centerof the broad innerface because at thatlo cation the current travels parallel to the seamand electrical losses are therefore negligible. The construction of theseam is such that there is a minimum of surface discontinuity on theinside, the lap of material being offset outwardly of the guide.Customary electroplatiug and molding techniques are' followed during theassembly of the guide with its fittings to produce a finished assemblywhich may be readily installed in an ultra high frequency transmissionline. Y I t In the use of this construction it is also possible to takeadvantage of the commercial availability of wide thin sheets of metalsuch as are accurately rolled for manufacturing andbuilding'construction'to make guides which are beyond the size rangepossible for seamless tube construction and without the objectionablehelical configuration with its extensive helical seam. Corrugationdepths may be produced to practically any limit within the limits ofelongation of preferred copper alloys.

The invention will be best understood by consideration of the drawingforming a part of this specification in which,

FIGURE 1 is a fragmentary longitudinal elevation view showing the guideof my invention in assembly with a wave guide end fitting, partially cutaway for clarity;

FIGURE 2 is an end elevation view of the guide assembly of FIGURE 1taken from the left hand end;

FIGURE 3 is a developed view of a strip of material as is used inproducing the wave guide of my invention, after corrugating but beforeinterfolding to rectangular form; and

FIGURE 4 is an end view of the guide of my invention after therectangular forming operations on the blank of FIGURE 3.

Referring to the drawings, FIGURE 1 shows a flexible wave guide assembly25 consisting of a flexible metal inner core 28 of rectangulartransverse configuration which forms the wave guide proper of theassembly. Flange fitting 29, illustrating a typical termination, issecured over the end of the guide as by soldering at 34 and the externalguide surface adjacent fitting 29 is covered with flexible molded layersof rubber or synthetic rubber 26, which serves as a mechanicalprotection and as a stabilizing member of the assembly. It will beunderstood that terminal fittings are employed at both ends of the guideand that various other types of fittings than as illustrated may be fortermination, depending upon the requirements of the circuit.

The guide inner core 28 is constructed with corrugations or undulationsin its side walls in order to permit a limited degree of flexing. Thisflexing may take place in one of two planes with respect to thelongitudinal axis of the guide, either of the long dimension or theshort dimension. The corrugation depth and shape may vary, a suitableguide being constructed by forming the corrugations so that they aresomewhat rectangular as shown in the drawing. The metal from which theguide is constructed is usually brass in the rangeof thickness of fromthree to thirty-five-thousandths of an inch, although the particularmaterial used, tl 1e size and specific shape of the corrugations may bevaried.

The corrugations of the inner core 28 are disposed at right angles tothe longitudinal axis of the guide and in the construction of such aguide I first form a flat, elongated blank 35 of a desired length, asillustrated in FIG- URE 3, having transverse corrugations 32 rolled orotherwise established therein. Advantageous methods of producing suchcorrugations are by progressive stamping operations utilizing a punchand die set or, an alternative method could be pursued using mated,opposed rolls, each of the rollers having a corrugated periphery, and bypassing the flat strip between such rolls.

When the blank has been corrugated as in FIGURE 3, it may then be formedas the rectangular tube or inner core 28, as in the end view of FIGURE4. Rectangular forming may be accomplished by first producing rightangle bends in the blank normal to the corrugations at the location ofthe corners of the tube and thereafter lapping and soldering or brazingthe seam as shown at 36 in FIGURE 4, with the lap offset outwardlythereby making for a minimum of internal surface discontinuity.Furthermore, the seam may be discontinuously soldered or brazedlongitudinally of the formed tube suflicient only to hold the tube infirm rectangular shape, and permit molding of the rubber covering 26; inwhich case a limited amount of twisting is available in the finishedguide. A butt joint may be substituted for the lap joint 36, however, Ihave found that the lap seam provides an accurate product with minimumtooling.

I locate the seam, as hereinbefore indicated, at the center of a broadinner face of the guide since, at that location, there is a null pointin the high frequency current pattern by reason of the fact that thecurrent travels axially of the guide, hence there is a minimum of lossfrom the seam as compared with known guides. having helical seamsperipherally disposed where the current must travel across each seam.

It will be noted by further observing FIGURE 2, that there is regularityof the undulation at the entrance to the guide and, while undulationsare present, theseare of a uniform pattern suitable to transmission ofultra high frequency current.

Having thus described my invention, 1 claim:

1. A flexible wave guide constructed in the form of a rectangular,longitudinally seamed tube and adapted, to the propagation therethroughof ultra high frequency wave energy, the side walls of the tube beingformed of a continuous series of uniformly spaced corrugations arrangedtransversely with respect to the longitudinaltube axis, the seam of thetube being electrically closed throughout its length, but structurallydiscontinuously closed and located centrally of a broad inner face whereultra high frequency current traveling in the tube is, parallel thereto,whereby electrical losses in propagation are efficiently curtailed.

2. A flexible waveguide assembly constructed, in part, in theform of arectangular, longitudinally seamed metal tube adapted to the propagationtherethrough of ultra high frequency wave energy, the side walls ofthetube being formed of a continuous series of uniformly spacedcorrugations arranged transversely with respect to the longitudinal tubeaxis, the seam of the tube being, electrically closed, butdiscontinuously mechanically closed throughout its length and waveguideterminal fittings secured at the ends of the tube.

References Cited in the file of this patent UNITED STATES PATENTS341,019 Kent May 4, 1886 343,024 Gordon et a1. June 1, 1886 1,811,678Smith June 23, 1931 2,006,925 Klemp July 2, 1935 2,115,441 Black Apr.26,. 1938 2,156,934 Barrett May 2, 1939 2,358,960 Cleve Sept. 26, 19442,441,081 Perry May 4, 1948 2,563,578 Candee Aug. 7, 1951 I UHMR no I.

